The present invention relates to an electrical machine such as, for example, an electric motor or a generator, comprising a stator and a rotor having a plurality of permanent magnets.
Electrical machines of this type are employed in a variety of technical applications. Inter alia, electric motors are known, in which the rotor has a plurality of magnet segments of a permanent magnetic material, which are fastened to a magnetic return ring. Conversely, the stator has a number of field coils, each of which are wound around a pole core. In an electric machine of this type, a specific ripple can be observed in the torque generated. This torque ripple, which manifests as an angle-dependent deviation in the motor torque at a constant current, is associated with the “cogging” of the motor, and is attributable to a magnetic interaction of the stator poles with the rotor poles. However, depending upon the field of application of the electrical machine, torque ripple, which is periodically superimposed on the shaft torque of the motor, can have a negative impact upon speed regulation and the working process. In such a case, a reduction of cogging and of torque ripple in the electrical machine is desirable. To this end, the end sections of the magnet segments can be deliberately shaped. For example, by means of the appropriate flattening of the end sections of the magnet segments, “detached pole portions” can be formed, which permit a more favorable magnetic transition between the magnet segments. In an arrangement of eight poles and eight segments, 16 detached pole portions are provided accordingly. If a further reduction of torque ripple or cogging is required, further structural measures must be adopted.